Parasitic worms come from two very different phyla-Platyhelminthes (flatwor
ms) and Nematoda (roundworms). Although both phyla possess nervous systems
with highly developed peptidergic components. there are key differences in
the structure and action of native neuropeptides in the two groups. For exa
mple, the most abundant neuropeptide known in platyhelminths is the pancrea
tic polypeptide-like neuropeptide F, whereas the most prevalent neuropeptid
es in nematodes an FMRFamide-related peptides (FaRPs), which are also prese
nt in platyhelminths. With respect to neuropeptide diversity, platyhelminth
species possess only one or two distinct FaRPs, whereas nematodes have upw
ards of 50 unique FaRPs. FaRP bioactivity in platyhelminths appears to be r
estricted to myoexcitation, whereas both excitatory and inhibitory effects
have been reported in nematodes. Recently interest has focused on the pepti
dergic signaling systems of both phyla because elucidation of these systems
will do much to clarify the basic biology of the worms and because the pep
tidergic systems hold the promise of yielding novel targets for a new gener
ation of antiparasitic drugs. (C) 1999 Elsevier Science Inc. All rights res
erved.